Output correct content-type with API responses.
Output correct content-type with API responses.

Fixes #281

ChengTiesheng/cadvisor,kmicheal/cadvisor,hacpai/cadvisor,kmicheal/cadvisor,mangalaman93/cadvisor,f0/cadvisor,hw-qiaolei/cadvisor,difro/cadvisor,dchen1107/cadvisor,atyenoria/cadvisor,jhjeong-kr/cadvisor,vishh/cadvisor,f0/cadvisor,bowlofstew/cadvisor,rajthilakmca/cadvisor,mr-justin/cadvisor,c-st/cadvisor,dchen1107/cadvisor,ChengTiesheng/cadvisor,erSitzt/cadvisor,guoshimin/cadvisor,ainsleyc/cadvisor,wulonghui/cadvisor,dchen1107/cadvisor,kateknister/cadvisor,jhjeong-kr/cadvisor,vmarmol/cadvisor,rjnagal/cadvisor,timstclair/cadvisor,datawisesystems/cadvisor,hzy001/cadvisor,ainsleyc/cadvisor,yifan-gu/cadvisor,kmicheal/cadvisor,mesosphere/cadvisor,afein/cadvisor,BrickXu/cadvisor,jmaitrehenry/cadvisor,aivarasko/cadvisor,derekwaynecarr/cadvisor,f0/cadvisor,carmark/cadvisor,hw-qiaolei/cadvisor,yolkov/cadvisor,jzaefferer/cadvisor,morpheyesh/cadvisor,bowlofstew/cadvisor,jimmidyson/cadvisor,shilpamayanna/cadvisor,megamsys/cadvisor,bing6/cadvisor,jhjeong-kr/cadvisor,megamsys/cadvisor,vegasbrianc/cadvisor,timstclair/cadvisor,bowlofstew/cadvisor,erSitzt/cadvisor,carmark/cadvisor,jimonreal/cadvisor,hacpai/cadvisor,guoshimin/cadvisor,shilpamayanna/cadvisor,aivarasko/cadvisor,dalanlan/cadvisor,dalanlan/cadvisor,vishh/cadvisor,hzy001/cadvisor,feiskyer/cadvisor,jimonreal/cadvisor,BrickXu/cadvisor,erSitzt/cadvisor,f0/cadvisor,pwittrock/cadvisor,normanjoyner/cadvisor,derekwaynecarr/cadvisor,yolkov/cadvisor,IFTTT/cadvisor,takecy/cadvisor,bpradipt/cadvisor,vegasbrianc/cadvisor,mangalaman93/cadvisor,difro/cadvisor,Snorch/cadvisor,jimmidyson/cadvisor,whosthatknocking/cadvisor,yifan-gu/cadvisor,vmarmol/cadvisor,Clever/cadvisor,takecy/cadvisor,morpheyesh/cadvisor,ncdc/cadvisor,aivarasko/cadvisor,vegasbrianc/cadvisor,rajthilakmca/cadvisor,bpradipt/cadvisor,linux-on-ibm-z/cadvisor,atyenoria/cadvisor,Clever/cadvisor,rjnagal/cadvisor,IFTTT/cadvisor,ncdc/cadvisor,derekwaynecarr/cadvisor,dchen1107/cadvisor,difro/cadvisor,jimmidyson/cadvisor,derwolfe/cadvisor,whosthatknocking/cadvisor,ncdc/cadvisor,BrickXu/cadvisor,atyenoria/cadvisor,vmarmol/cadvisor,ainsleyc/cadvisor,Snorch/cadvisor,datawisesystems/cadvisor,hacpai/cadvisor,jmaitrehenry/cadvisor,IFTTT/cadvisor,anarcher/cadvisor,timstclair/cadvisor,ncdc/cadvisor,pwittrock/cadvisor,jhjeong-kr/cadvisor,cnaize/cadvisor,wulonghui/cadvisor,guoshimin/cadvisor,yolkov/cadvisor,feiskyer/cadvisor,jzaefferer/cadvisor,dalanlan/cadvisor,kateknister/cadvisor,anarcher/cadvisor,erSitzt/cadvisor,Clever/cadvisor,Snorch/cadvisor,CrazyJvm/cadvisor,f0/cadvisor,yifan-gu/cadvisor,bing6/cadvisor,normanjoyner/cadvisor,jimonreal/cadvisor,hzy001/cadvisor,jmaitrehenry/cadvisor,cnaize/cadvisor,dchen1107/cadvisor,pwittrock/cadvisor,derekwaynecarr/cadvisor,anarcher/cadvisor,BrickXu/cadvisor,afein/cadvisor,cnaize/cadvisor,BrickXu/cadvisor,derekwaynecarr/cadvisor,rajthilakmca/cadvisor,jzaefferer/cadvisor,linux-on-ibm-z/cadvisor,mangalaman93/cadvisor,hw-qiaolei/cadvisor,mesosphere/cadvisor,CrazyJvm/cadvisor,erSitzt/cadvisor,kateknister/cadvisor,derwolfe/cadvisor,IFTTT/cadvisor,takecy/cadvisor,derwolfe/cadvisor,c-st/cadvisor,c-st/cadvisor,ncdc/cadvisor,mesosphere/cadvisor,bing6/cadvisor,bpradipt/cadvisor,IFTTT/cadvisor,ainsleyc/cadvisor,feiskyer/cadvisor,rjnagal/cadvisor,wulonghui/cadvisor,mr-justin/cadvisor,vishh/cadvisor,jhjeong-kr/cadvisor,mr-justin/cadvisor,ChengTiesheng/cadvisor,whosthatknocking/cadvisor,linux-on-ibm-z/cadvisor,CrazyJvm/cadvisor